nuclear chemistry chapter 10 modified from mrs. wolfe
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- Nuclear Chemistry Chapter 10 Modified from Mrs. Wolfe
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- Isotopes Recall that the mass number is the SUM of the protons + neutrons Isotopes are atoms on an element that have different numbers of neutrons. Why is the atomic mass a decimal? The average of the masses of an elements different isotopes.
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- Isotope Notation Atomic Number = Protons only Mass Number Protons +neutrons Isotopes
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- Recall that atoms look like this Protons (positive) Neutrons (neutral) Both in the nucleus Electrons (negative) Surround the nucleus neutron electron proton nucleus orbit of electron
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- Recall what an isotope is When an element gains or loses a neutron it becomes an isotope of that element. Still the same element because the atomic number has not changed (atomic number is the number of protons) neutron electron proton nucleus orbit of electron
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- Radioactivity Radioactive materials have UNSTABLE nuclei. Isotopes are generally radioactive. Why do you think that is? Because isotopes have unstable nuclei, since they have a WEIRD number of neutrons.
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- What causes a nucleus to be unstable? Unstable = radioactive When the strong nuclear force cannot overcome the electrostatic force repelling the protons away from each other in the nucleus, the nucleus becomes unstable.
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- What is the Strong Nuclear Force? The attractive force that binds the protons and the neutrons together inside the nucleus. It acts among protons, among neutrons, and between protons & neutrons
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- Unstable atoms tend to become stable! They will get rid of neutrons to stabilize themselves! Very similar to bailing water out of a sinking boat to keep it from sinking! The process of becoming stable is called RADIOACTIVE DECAY.
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- Radioactive DECAY The process of emitting particles/energy to become stable is known as Radioactive Decay. It s NOT ROTTING!
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- 3 Types of Radioactive Decay Alpha Protons and Neutrons are emitted Beta Electron emitted Gamma Burst of energy is emitted
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- Radioactive Decay is Spontaneous.
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- Penetrating Power of Radioactivity Alpha Particles LARGE, heavy protons/neutrons can t travel far. can be blocked by the dead skin layer on your hand or a thin sheet of paper Beta Particles SMALL, light electrons can travel farther. can be blocked with a thin sheet of lead Gamma Particles Energy can travel very far. can be blocked with thick lead or concrete. paper lead concrete
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- How can we detect radioactive decay? Geiger Counters! Go get the handout for this LAB (it requires a computer with Shockwave on it the MacBook Airs have this)
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- Think about this: Why do you have to wear a LEAD apron during an X-Ray? Because X-Rays are GAMMA particles that are and used to photograph our bones. A LEAD apron will protect the fragile parts of your body that we don t want to expose to the X-rays.
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- Where does radioactivity come from? Isotopes from the Sun Isotopes in Dirt & Rocks Isotopes in the Air! Isotopes in YOU! Isotopes in Food/Water Just about EVERYTHING! This is called Background Radiation because you re exposed to it everyday.
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- How much of a Radiation Dose do you receive on a yearly basis? An annual dose under 350 mrem is natural and safe. Let s figure out your annual dose! Time for a WS! Estimate Your Personal Radiation Dose IMPORTANT: You need the info. below for the WS! The elevation you live at is 0-1000 ft. Your home is made of wood. You DO NOT live within 50 miles of any power plant.
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- When atoms emit PROTONS... they are no longer the same element. Example: A Lead isotope is an alpha source, so it loses protons and neutrons. If it loses 3 protons, it s atomic number changes from 82 to 79. What element did it change to? Gold!! Now, this is a CHEMICAL change, not a physical change. So it won t LOOK LIKE gold, but it will ACT LIKE gold!
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- What about if neutrons/energy are lost? It is still the same element, but with less MASS. Example: An isotope of Lead emits a neutron. Its atomic NUMBER is still 82, but its atomic MASS has changed from 207 to 206. Because its atomic NUMBER doesn t change, it s still Lead! It s Lead-206 (206 tells you the MASS of the isotope)
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- Rates of Becoming Stable How quickly/slowly do atoms stabilize? It s specific to each isotope.
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- IsotopeStabilization Rate Uranium-2384,510,000,000 years Potassium-401,280,000,000 years Radium-2261,599 years Radon-2223.82 days Thorium-2190.00000105 sec
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- Half-life Half-life the amount of TIME required for HALF of a radioactive substance to stabilize. Example: The half-life of Iodine-131 is 8 days. If you start with 50 grams of Iodine-131, then 25 grams will remain radioactive after 8 days. During another half-life, half of the remaining radioactive substance will stabilize. How much Iodine remains radioactive after 16 days? 12.5 grams Time for a WS! Half-life Calculation WS
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- Half-lives&stabilizing atoms! Tennis player = radioactive substance Little girl = Stabilized atoms Remember, half-life is the amount of TIME required for HALF of the substance to STABILIZE.
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- Let s Take A Closer Look
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- Practice Question What color represents theradioactive element? RED What color represents the stable element? BLUE
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- Time for a LAB! If you havent done the Skittle Labbe sure to do it to better understand how to create and interpret a Half-Life graph!
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- Carbon-dating C-14 is a naturally- occurring isotope found in the tissue of living things. It can be used to determine how long a living thing has been dead! This is called Carbon- dating.
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- How does Carbon-Dating work? 1. The sun puts C-14 in our air. 2. Plants take in the C-14. Animals eat plants. 3. Humans eat the C-14 in plants/animals. 4. The C-14 naturally decays. As long as the human keeps eating, the C-14 supply in the body is replenished. 5. Human dies and stops eating. The C-14 supply is not replenished. 6. The decay rate of C-14 is known. We can use it to figure out how long the human has been dead.
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- Carbon-Dating in Forensics C-14 has a half-life of 5,715 years. You find a body that has 500 g of C-14 left. You know this body had 1000 g of C-14 when he/she died because the air holds that amount of C-14. How long has this person been dead? 5,715 years!
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- Nuclear Fission So far, we ve discussed atoms EMITTING particles. Sometimes, a nucleus has to SPLIT to release particles/energy. FISSION is the process of splitting a nucleus to release energy
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- Nuclear Fusion Fusion is the process of JOINING two nuclei. This happens in the sun, when two Hydrogen atoms FUSE & release light energy!
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- The picture below illustrates. .FISSION!
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- A single neutron begins a Fission chain reaction and makes LOTS of energy!
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- Nuclear Power Plants 104 Nuclear Plants in the US 20% of electricity 1 gram Uranium-235 = 3 tons of coal!!
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- How does a Nuclear Reactor Work? A neutron begins a FISSION chain reaction in the reactor vessel. Control rods are used to capture neutrons to control the reaction speed. Energy released from fission heats a chamber of water. The water boils and becomes steam. The steam turns a turbine and creates electricity. The steam is CONDENSED back into liquid by cold water pumped in from a nearby pond. THE RADIOACTIVE MATERIALS NEVER MIX WITH THE POND WATER.
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- Pressurized Water Reactor
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- Boiling Water Reactor
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- Fission Reactor
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- What dangers do they present? What do we do with the toxic waste after fission? Right now, it s kept on Yucca Mountain, Colorado. Thermal Pollution (in ponds around reactors) Warmer water used in the condenser is returned to ponds. Uranium-235 is a limited resource. Chance of Meltdown (Particles/energy could accidentally be released from the reactor vessel and out into the opencalled fallout .)
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- Fusion Reactors Tokamak Fusion Test Reactor Princeton University National Spherical Torus Experiment
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- Fusion isn t used in power plants. It takes a LOT of energy to cause atoms to fuse. Energy is released when they fuse, but it s not much more than it took to start the fusion process. There s no chain reaction. So it won t work for a power plant.
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- Nuclear Applications Was t
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